The primary purpose of this project is to conduct a comprehensive in vivo investigation of the immunosuppressive properties of the newly identified lymphocyte chalone. The protocol is designed to evaluate this agent by a progressively sophisticated sequence of transplantation studies carried out in parallel with investigations of its immunologic mechanisms of action. Concomitant studies are designed to characterize the limitations and restrictions and toxicity of the lymphocyte chalone in organ allotransplantation. The ultimate objective of these endeavors is to make available a safer and more effective agent for control of transplant rejection in human recipients of vital organ allografts. The lack of cytotoxicity and specificity of immunologic action of the lymphocyte chalone suggest exceptional advantages to the pediatric patient. The information generated from these investigations should add a new dimension to our existing body of knowledge of transplantation biology.